DE3810678C2 - Permanent magnet with high coercive force and high maximum energy product and process for its production - Google Patents

Description

The invention relates to a permanent magnet, which as Main components are iron, platinum and niobium and less than Contains 0.5 atomic% of impurities, the Permanent magnet a high coercive force and very has large maximum energy product.  

From DE 31 44 869 is a permanent magnet made from 34 to 39.5 atomic% platinum, Balance iron and less than 0.5% impurity Alloy with high coercive force and high maximum energy A product based on a binary iron-platinum excess structure alloy with a homogeneous dispersion of geord neten γ₁ phase of the face-centered tetragonal type in a matrix of the disordered γ phase from the surface known cubic type. The well-known alloy is at 900 to 1400 ° C and 1 minute to 100 hours homogeneous siert, then in water or air at 30 ° C / minute to Quenched 2000 ° C / second, at 400 to 700 ° C during Reheated for 1 minute to 100 hours and then cooled.

The object of the invention is to achieve the maximum To further increase energy product.

This task is accomplished by a permanent magnet Claim 1 solved.

The permanent magnet according to the invention has a coercive force of more than 39 800 A · m ^-1 , a residual magnetic flux density of more than 0.5 T and a maximum energy product of more than 39.8 KJ · m ^-3 .

A method of manufacturing the permanent magnet according to the invention is that one

• a) the alloy at 900 to 1400 ° C for 1 minute to 10 Hours of homogenization annealing,
• b) the alloy quickly at 30 ° C / min to 2000 ° C / sec discourages
• c) the alloy then at 450 to 800 ° C for 1 minute reheated up to 500 hours and
• d) then cools down.

Another method is a step b1) between quenching b) and Reheat c) the alloy made at one plastic processing of the alloy with a Reduction ratio of more than 80%. This Plastic processing can be wire drawing or rolling his.

According to one embodiment, the reheating takes place after Process step c) at 550 to 750 ° C.

Under the aforementioned incomplete gamma 1 single phase  either by the alloy composition or achieved by the heat treatment is as follows understand: While the Fe-Pt binary alloy one has a fully ordered grid if the Composition Fe: Pt equal to 50:50, expressed by the Number of atoms that is used in the present invention the iron content of the alloy increases somewhat under formation of the incompletely ordered grid of the gamma 1 phase. The incomplete gamma 1 phase can be obtained using a heat treatment that is either quenching alone comprises or a combination of quenching and then reheating, the heat treatment the initial stage of the transformation from the gamma phase to the gamma 1 phase of the ordered grid.

Becomes a permanent magnet using an alloy the aforementioned composition according to one of the aforementioned Process formed, then the crystal structure of the Alloy magnets either one of the following Phases or two phases: the incomplete gamma 1 single phase of the face-centered, tetragonal Systems lies due to either the alloy composition or the heat treatment applied to the alloy before, and the two phases are made up of a gamma phase matrix of the face-centered cubic system and one homogeneous dispersed fine precipitate from the gamma 1 phase educated. Regardless of whether a single-phase or The permanent magnet has a two-phase structure the desired magnetic properties according to the invention on.  

The details of the invention are as follows Production of the aforementioned permanent magnet stage for Level described.

(A) The starting materials are measured so that they make a metal mixture that is a composition from 48 to 66.9 atomic% iron, 33 to 47 atomic% platinum, 0.1 up to 10 atomic% niobium and less than 0.5 atomic% impurities having. The metal mixture is placed in a suitable oven melted and stirred thoroughly to make a melted one Obtain alloy with a homogeneous composition. Then an alloy body is made using a suitable shape, and this can then be in the be brought into the desired shape, e.g. B. by wire drawing, Forging or rolling. The alloy body becomes 900 to 1400 ° C for 1 minute to 10 hours for homogenization glow heated and then with a high speed of faster than 30 ° C / min. but slower than 2000 ° C / sec. deterred. The quenching process will performed one of the following structures at room temperature to stabilize: namely a structure that Initial stage of transformation from the gamma phase of the face centered cubic system to the gamma 1 phase of the face-centered, tetragonal system corresponds to or a structure that is formed by fine Precipitation of the gamma 1 phase of the ordered lattice homogeneous in the gamma phase matrix of the disordered lattice are dispersed.  

(B) After quenching the above step (A) the alloy body at 450 to 800 ° C and preferably 550 to 750 ° C for 1 minute to 500 hours and preferably reheated for 5 minutes to 100 hours, under Formation of local tensions in the solid solution, which is the initial stage of the transformation from the disordered gamma phase to the ordered lattice of the gamma 1 phase mean, this transformation in the high temperature takes place. In this way, one Dislocation of the magnetic domain in the alloy body prevented and a permanent magnet with both one ultra high coercive force and a very high maximum Energy product trained.

(C) Alternatively, after quenching in the Step (A) is a plastic treatment with a Reduction ratio of greater than 80% on that Perform alloy body, e.g. B. by wire drawing or by rolling.

(D) After plastic processing in step (C) the alloy body is annealed by the Reheat according to step (B) above. At this tempering causes the internal tensions that during plastic processing in the above stage (C) have been trained, training appropriate local Tensions and of crystalline aggregate structures in the course the transformation into the gamma 1 phase. This will make the Tendency towards right-angled, magnetic Hysteresis curve increases and results in a permanent magnet with excellent magnetic properties.  

Below are the reasons why the composition of the alloy has been selected in the aforementioned manner is explained:

Fe: 48 to 66.9 atomic%

Basically, the present invention magnetic properties of a binary Fe-Pt alloy with an equal atomic proportion by increasing the iron content improved. If the iron content is less than 48 atomic%, then the ratio of Fe and Pt in the Alloy composition, expressed by atomic%, 50:50, and the magnetic properties of the alloy bad. On the other hand, if the iron content is 66.9 atomic% then the alloy tends to be its magnetic Properties to lose. Therefore a share of 48 to 66.9 atomic% iron selected.

Pt: 33 to 47 atomic%

If the platinum content is less than 33 atomic%, it loses the alloy has its magnetic properties. If on the other hand the platinum content exceeds 47 atomic%, then approaches the ratio of Fe and Pt in the alloy composition, expressed as atomic%, 50:50, and the magnetic Properties of the alloy deteriorate. That's why 33 to 47 atomic% Pt were selected.

Nb: 0.1 to 10 atomic%

Niobium improves the reproducibility of the magnetic  Properties. If the niobium content is less than 0.1 atomic%, then you can get the desired reproducibility do not achieve. On the other hand, the niobium content exceeds 10 atomic%, then the magnetic deteriorate Properties of the alloy. Therefore, 0.1 to 10 atomic% Nb chosen.

The platinum content is preferably 34 to 43 atomic%. and the niobium content 0.3 to 5 atomic%.

The conditions for homogenization annealing according to the present invention are as follows explained.

At the temperature for the homogenization annealing it must be taken into account that the Order-disorder transformation point of the alloy with the composition according to the invention is 800 to 900 ° C, depending on the composition and that the Melting point is about 1550 ° C. Is the temperature for homogenization annealing below 900 ° C, then the gamma 1 phase of the ordered grid remains get, and you don't get the single gamma phase of disordered grid. On the other hand, if the treatment temperature is above 1400 ° C, i.e. close to the melting point, melts the alloy. Therefore the range of 900 to 1400 ° C for homogenization annealing chosen.

Is the duration of the homogenization annealing less than 1 minute, then you get a satisfactory one  Homogeneity does not exist even when the temperature of the treatment Is 1400 ° C. On the other hand, it gives a 10 hour Homogenization heat treatment adequate Homogeneity even when the treatment temperature is 900 ° C is, so treatment lasting longer than 10 hours takes no more meaningful improvement. For this The reason is a duration of 1 minute to 10 hours for the homogenization heat treatment selected.

Regarding the cooling rate from the high Homogenization annealing temperature applies: the faster the better. Is the cooling rate less than 30 ° C / min., then the dispersed, fine precipitation of the gamma 1 phase of the ordered lattice to grow into very large gamma 1 phase crystals and hinder the improvement of magnetic properties. The upper limit for the cooling rate is with 200 ° C / sec. stated because this is roughly the technical Limit on quenching involves and you get no improvement can expect if you go even faster than this top one Border cools down. That is why the cooling speed is too 30 ° C / min. up to 2000 ° C / sec. for cooling off the high Homogenization annealing temperature chosen.

The following are the conditions for reheating described for tempering after quenching. Is that Reheat temperature below 450 ° C, then the Reheat time required to get the desired one To achieve tempering effect, too long, d. H. it is more than 500 hours. Such a long heating is uneconomical,  and any meaningful improvement in magnetic Properties cannot be expected. Lies on the other hand the reheating temperature at more than 800 ° C, then there is a tendency for an ordered lattice forms, and this makes poorer magnetic Properties trained. Therefore, a range of 450 to 800 ° C selected for annealing. A special one the preferred range is 550 to 750 ° C.

If the reheating is less than 1 minute, then a sufficient temperature to improve the magnetic properties even if the temperature of the reheating is 800 ° C. On the other hand persists when reheated for more than 500 hours the tendency that the formation of an orderly Grid accelerates, improving magnetic Properties is hindered. That's why you choose a duration from 1 minute to 500 hours for reheating the temperature treatment.

Will plastic processing, such as wire drawing or rolling, carried out before annealing and this is Reduction ratio less than 80%, then the internal stresses that are associated with such a plastic Processing can be expected to be too low to the magnetic To improve properties. Therefore the reduction ratio chosen for the plastic processing to more than 80%.

The cooling at the end of the reheating for annealing can done either quickly or slowly, but being a fast one  Cooling is preferred.

For better understanding, see the attached figures referred. It shows

Fig. 1 is a graph in which the relation between the reheating temperature and the magnetic properties of three types of alloys, containing 37 to 40 atomic% of platinum and 0.5 atomic% of niobium is shown;

FIG. 2 is a graph showing the relationship between the reheating conditions, that is, the temperature and the duration and the magnetic properties for the sample No. 8 of a compound of the invention, which sample is a typical example of a compound of the invention, and FIG. 39 , 5 atomic% platinum and 0.5 atomic% niobium;

Fig. 3, 4 and 5 diagrams showing the relationship between the composition and magnetic properties of the Fe-Pt-Nb ternary alloys according to the invention;

Fig. 6 is a demagnetization curve of the abovementioned sample No. 8 of the alloy according to the invention after the annealing under the condition (a) shown in Table 1, which will be described below. and

Fig. 7 shows an alloy composition diagram in which the range of the alloy composition of the invention is shown shaded in accordance with.

Preferred embodiments are shown below.

Samples of alloys with the composition according to Table 1 was in the following manner Use of electrolyte iron with a purity of 99.9% platinum and niobium manufactured. 10 g of the starting materials overall with the desired composition measured and placed in an alumina Tamman tube and the materials were melted in a Tamman furnace, whereby argon gas was passed through. The melt was thoroughly stirred to form a homogeneous molten alloy, and the alloy melt was in a quartz tube with a diameter of 2.0 to 3.8 mm sucked in to form a round alloy rod. In the same way, round alloy rods for different alloy compositions, like them shown in Table 1. The samples for  the different alloys were obtained by using the cut round alloy rods with a length of 25 mm.

The samples were heated by heating at 900 to 1400 ° C during Homogenized for 1 hour, and the homogenized samples were either with water or by air cooling deterred. Some of the samples were tested after the Quenching but without tempering while other samples annealed under the conditions given in Table 1 before the test was done.

The samples treated in this way were magnetic Properties examined. Samples 2, 3 and 14 according to Table 1 was drawn into wires after quenching and were then annealed and tested. The results of the Exams are also shown in Table 1.  

Table 1

Table 1 shows that the samples with the composition according to the invention, under the conditions treated the invention, an ultra-high Coercive force, a high residual magnetic flux density and have a very large maximum energy product.

Fig. 1 shows the effect of annealing on the magnetic properties for three samples with different alloy composition: Sample No. 3 (Fe-37 Pt-0.5 Nb), No. 6 (Fe-38.5 Pt-0,.. 5 Nb) and No. 9 (Fe-40 Pt-0.5 Nb). These three samples were all annealed at the same time, namely 2 hours, at different temperatures in the range from 500 to 750 ° C. From the figure it can be seen that the annealing temperature varied to achieve a high coercive force depending on the alloy composition. In the case of Sample Nos. 6 and 9, which had platinum contents of 38.5 atom% and 40 atom%, respectively, the quenching alone gave a quite good coercive force, with annealing achieving a further improvement in the coercive force.

From Table 1 and Fig. 2 it can be seen that of the tested samples, sample No. 8 (Fe-39.5 Pt-0.5 Nb) had the largest maximum energy product. The inventors found that Sample No. 8 had an extremely large maximum energy product of 26 KJ · m ^-3 when cooled to a very low temperature (-196 ° C) using liquid nitrogen.

It should be noted that plastic processing is possible with the alloys according to the invention. The Experiments have shown that permanent magnets that pass through plastic processing have been trained, better exhibited magnetic properties as such, at where there is no plastic processing.

Fig. 2 shows the relationship between the magnetic properties and the conditions of constant temperature annealing, that is, the heating temperature and the duration, for the sample No. 8 (Fe-39.5 Pt-0.5 Nb), which is a typical of the present invention Represents alloy. In this sample, when the temperature of annealing is low, a long period of the heating treatment is required to obtain good magnetic properties.

Fig. 3 shows the relationship between the compositions of the Fe-Pt-Nb ternary alloys and the coercive forces. Fig. 4 shows the relationship between the compositions of the Fe-Pt-Nb ternary alloys and their residual magnetic flux densities. Fig. 5 shows the relationship between the compositions of the Fe-Pt-Nb ternary alloys and their maximum energy products.

Figure 6 shows the demagnetization curve for Sample No. 8 (Fe-39.5 Pt-0.5 Nb), which had a high residual magnetic flux density and coercive force and whose maximum energy product was the largest of all tested samples. Alloy # 8 was easy to work with and was found to be suitable for both small magnets of complex shapes and magnets that are suitable at a temperature well below room temperature.

The shaded area of FIG. 7 outlines the composition of the alloy for the permanent magnets according to the invention.

Claims (5)

1. Permanent magnet made of a platinum and iron-containing alloy with a high coercive force and a high maximum energy product, the crystal structure being either an incomplete γ₁ phase of the face-centered tetragonal type or a two-phase system with a homogeneous dispersion of the face-centered tetragonal γ₁ phase in a face-centered matrix cubic γ phase, characterized in that the alloy consists of 48 to 66.9 atomic% iron, 33 to 47 atomic% platinum, 0.1 to 10 atomic% niobium and less than 0.5 atomic% impurity gene exists. 2. A method for producing a permanent magnet according to claim 1, characterized by

• a) a homogenization annealing of the alloy at 900 to 1400 ° C. for 1 minute to 10 hours,
• b) rapid quenching of the alloy at 30 ° C / min to 2000 ° C / sec,
• c) reheating the alloy at 450 to 800 ° C for 1 minute to 500 hours and
• d) a final cooling.

3. The method according to claim 2, characterized by

• b1) plastic processing of the alloy with a reduction ratio of more than 80%, this additional process step between quenching (b) and reheating (c) of the alloy.

4. The method according to claim 3, characterized in that plastic processing by wire drawing or rolling he follows. 5. The method according to claim 2, characterized in that reheating after process step (c) at 550 to 750 ° C takes place.